Microelectromechanical systems (MEMS) have recently been developed as alternatives for conventional electromechanical devices such as relays, actuators, valves and sensors. MEMS devices are potentially low cost devices due to the use of microelectronic fabrication techniques. New functionality may also be provided because MEMS devices can be much smaller than conventional electromechanical devices.
Many applications of MEMS technology use MEMS actuators. For example, many sensors, valves and positioners use actuators for movement.
MEMS devices have relied upon various techniques to provide the force necessary to cause the desired motion within the microstructures. For example, cantilevers have been employed to transmit mechanical force in order to rotate micromachined springs and gears. In addition, some micromotors are driven by electromagnetic fields, while other micromachined structures are activated by piezoelectric or electrostatic forces. Recently, MEMS devices that are actuated by the controlled thermal expansion of an actuator or other MEMS components have been developed.
There are two fundamental techniques for electro-thermal actuation. One technique uses a bimorph structure, i.e., a cantilever beam made of two different materials, and the other uses two arms, or beams, of varying cross-sectional area connected at a distal end as shown in FIG. 1. When current is passed in the two arms, the arms elongate to different lengths because of their different cross-sections and thus deflect the distal end of the actuator in one direction as shown in FIG. 2. With reference to FIG. 1, the actuator 10 has a hot arm 12 which is the thinner arm and a cold arm 14. The terms hot and cold are used in a relative sense. As shown by the arrow, because the hot arm 12 is smaller in cross-section than the cold arm 14, it has a higher resistance and thus heats up and expands more to cause the distal end 16 of the actuator to bend in one direction. Thermally actuated MEMS devices that rely on thermal expansion of the actuator have recently been developed to provide for actuation in-plane, i.e., displacement along a plane generally parallel to the surface of the microelectronic substrate.
Notwithstanding the MEMS actuators that have previously been proposed, a number of existing and contemplated MEMS systems, such as relays, actuators, valves and sensors require more sophisticated actuators that provide useful forces and displacements while consuming reasonable amounts of power in an efficient manner. Since it is desirable that the resulting MEMS systems be fabricated with batch processing, it is also preferred that the microelectronic fabrication techniques for manufacturing the resulting MEMS systems be affordable, repeatable and reliable.
It is desirable to provide an actuator that increases and improves the displacement produced by thermal actuation techniques. In addition, it is desirable to provide an actuator that can be deflected in multiple directions.
According to a first aspect of the invention, there is provided a microelectromechanical structure. The structure includes a substrate, a first beam, a second beam and a connector. The substrate defines a reference plane. The first beam has a proximal end and a distal end. The proximal end of the first beam is coupled to the substrate wherein the first beam extends in a first plane parallel with the reference plane. The first beam includes three layers including a dielectric layer sandwiched between two conductive layers. The second beam also has a proximate and a distal end. The proximal end of the second beam is coupled to the substrate wherein the second beam extends in the first plane parallel with the reference plane. The connector defines a distal end of the structure and couples the distal end of the first beam to the distal end of the second beam. A potential difference is applied between the two conductive layers of the first beam so that current flows into one conductive layer and out the other conductive layer and no potential difference is applied across the second beam.
According to a second aspect of the invention, there is provided a microelectromechanical structure. The structure includes a substrate and an actuator. The substrate defines a reference plane. The actuator has a portion thereof suspended above the reference plane of the substrate. The actuator includes a hot arm having a distal end, the hot arm is made of three layers including a dielectric layer sandwiched between two conductive layers and a cold arm having a distal end which is coupled to the distal end of the hot arm. A potential difference is applied across the hot arm so that a current circulates through the conductive layers of the hot arm to cause the hot arm to expand and move the distal ends of the hot and cold arms towards the contact located on the substrate.
According to a third aspect of the invention, there is provided a microelectromechanical device. The device includes a substrate, a first beam, a second beam and a connector. The substrate defines a reference plane. The first beam has a proximal and a distal end. The proximal end of the first beam is coupled to the substrate wherein the first beam extends in a plane parallel with the reference plane. The first beam is formed by a three layer structure having a dielectric layer sandwiched between two conductive layers. The second beam has a proximal and a distal end. The proximal end of the second beam is coupled to the substrate wherein the second beam extends in a plane parallel with the reference plane. The second beam is formed by a three layer structure having a dielectric layer sandwiched between two conductive layers. The connector couples the distal end of the first beam to the distal end of the second beam. A potential difference is applied across the first beam and no potential difference is applied across the second beam, thereby causing greater thermal expansion in the first beam resulting in deflection of the distal ends of the first and second beams.
For a further understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. In the following drawings, like reference numerals designate like or similar parts throughout the drawings.